This campaigner is rightly credited with leading the charge to end the Slave Trade in 1807, but in Britain's he's wrongly credited with ending slavery itself, which didn't happen until 1833. Granville Sharp differed from Wilberforce in that Sharp insisted on nothing less than the abolition of slavery itself. However, Wilberforce was only really interested in ending the slave trade, and when that ended, so did Wilberforce's fervour....
After 1807, the pro-slavery lobby proposed a policy of Amelioration, which would mean that slave owners would start treating their slaves better, and this would eventually lead to slavery dying out. Surprisingly, Wilberforce bought this idea, because he was also wrongly convinced that once the slaves got their freedom, they would go about slaughtering all the white people in the various British Caribbean islands. He made his feelings clear from the very beginning, when he joined the anti-slavery movement in the mid-1780s, and In 1793 Cugoano upset William Wilberforce by describing him as a hypocrite when he refused to support the campaign to end slavery in the British Empire.
Eventually, events left an ageing Wilberforce behind, and the Act to abolish slavery itself was passed in 1833, following revolts around the Caribbean, including the Sam Sharpe revolt in Montego Bay in 1832, when slaves alleged that the king had granted them their freedom, and that the white slave owners were illegally holding them in servitude.
So, maybe when Britain commemorates the ending of slavery, they should really honour Granville Sharp.